/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/DynamicMeshChangeTracker.h
Store IDs of saved triangles in TrianglesOut. if bInitial=true, old triangles are stored, otherwise new triangles
void GetSavedTriangleList ( [TArray](API\Runtime\Core\Containers\TArray)< int > & TrianglesOut, bool bInitial ) const